Method of production of cast polyamides

ABSTRACT

The present invention relates to a new method of production of cast polyamides.

The present invention relates to a new method of production of castpolyamides.

Cast polyamides are particularly high-molecular polyamides. In theproduction of cast polyamides, a lactam is poured into a mould togetherwith at least one catalyst and at least one activator and thenpolymerized anionically in this mould. The starting compounds present inthe mould are generally polymerized under the action of heat. Thisresults in a homogeneous material, which is superior to extrudedpolyamides with respect to crystallinity.

Cast polyamides are suitable as thermoplastic polymers for themanufacture of complex components. In contrast to many otherthermoplastics, they do not need to be melted, but are formed bypressureless anionic polymerization of a lactam in a mould at 120 to150° C. in just a few minutes. All known casting processes can be used,such as gravity casting, rotational casting and centrifugal casting. Ineach case the end product obtained comprises mouldings of ahigh-molecular, crystalline polyamide, which is characterized by lowweight, high mechanical strength, very good sliding properties andexcellent resistance to chemicals, and—because mould filling does nottake place under pressure—has only small internal stresses. Castpolyamides can be sawn, drilled, milled, ground, welded and printed orpainted; as well as complex hollow shapes, it is also possible forexample to use this polymer for making rollers for passenger lifts andsemifinished products, for example tubes, rods and plates for machineconstruction and for the automobile industry.

The production of cast polyamide parts starting from low-viscositylactam melts and a catalyst and an activator by so-called activatedanionic polymerization is known per se. For this purpose, usually twomixtures of catalyst and lactam or activator and lactam are preparedfresh in the form of a liquid melt separately from one another beforepolymerization, are mixed together immediately and then polymerized inthe mould. This should ensure that no undesirable reaction occursbeforehand.

As the catalysts/activators are only required in small amounts,proportioning is difficult. Inaccurate proportioning leads to largefluctuations in product quality and therefore to defective batches.Moreover, the activator/catalyst suffers when it comes repeatedly intocontact with air and moisture. Therefore it is also desirable from thestandpoint of workplace hygiene to prepare the activator and/or catalystin a different, safer manner.

One problem to be solved by the present invention is therefore toprovide a cost-effective and efficient method, which does not have thedisadvantages of the prior art.

It has now been found, surprisingly, that mixtures of at least oneactivator in at least one lactam and optionally at least one catalyst inat least one lactam, while complying with certain concentration limits,can in fact be produced, isolated and stored, and more easily, and canbe used as so-called BATCH-READY® lactam in the concentrations desiredfor polymerization. This high constancy of quality of the Batch-Ready®products can be attributed to the extremely precise initial weights ofthe individual constituents and the subsequent facilitated proportioningof the homogenized mixture. The proportioning measures for very smallamounts, which are critical for the criteria of quality and laboursafety, therefore no longer apply.

The present invention therefore relates to a new method of production ofcast polyamides by polymerization of lactams in the presence of at leastone activator and at least one catalyst, according to which

-   -   a) the activator is added in an amount of a max. 5 wt %,        preferably max. 2 wt %, especially preferably 0.1 wt % up to        less than 1 wt % mixture in at least one lactam melt at        temperatures between 70 and 120° C., preferably 80-100° C.,        homogenized and isolated after production, optionally dried,        packed and stored, or pelletized on a pelletizing belt or flaked        on a flaking roll and    -   b) the catalyst is added in an amount of a max. 5 wt %,        preferably 0.2 wt % of to less than 2 wt %, especially        preferably 1 wt % up to less than 2 wt % in at least one lactam        melt at temperatures between 70 and 120° C., preferably 80-100°        C., homogenized and pelletized on a pelletizing belt or flaked        on a flaking roll,        these melts of, a) and b) are mixed together and then are        polymerized in the mould at temperatures between 80 and 160° C.

In one embodiment of the invention the activator is added in an amountof a max. 5 wt %, preferably max. 2 wt %, especially preferably 0.1 wt %up to less than 1 wt % mixture in at least one lactam melt attemperatures between 70 and 120° C., preferably 80-100° C., homogenizedand isolated after production, dried, packed and stored

In another embodiment of the invention the activator is added in anamount of a max. 5 wt %, preferably max. 2 wt %, especially preferably0.1 wt % up to less than 1 wt % mixture in at least one lactam melt attemperatures between 70 and 120° C., preferably 80-100° C., homogenizedand isolated after production, packed and stored.

Compounds of general formula (I)

can be used as lactam in the sense of the invention, where R representsan alkylene group with 3 to 13 carbon atoms. Preferably it iscaprolactam and/or laurolactam. These are available commercially, e.g.from the company Lanxess Deutschland GmbH.

Isocyanates, isocyanurates, biurets, allophanates, uretdiones and/orcarbodiimides, as the individual compound or as a mixture, can be usedas activators in the sense of the invention. Activators that are blockede.g. with lactams, especially preferably caprolactam, or with phenols,oximes and/or epoxides and/or also activators containing solvents, canalso be used in the sense of the invention. The following are suitableas solvents: N-alkylpyrrolidones, e.g. N-methylpyrrolidone andN-ethylpyrrolidone, polyglycols such as polyglycol DME 200, dipropyleneglycol DME or tetraethylene glycol DME. These are commercially availableproducts, which are obtainable for example from the company Clariant.

Isocyanates in the sense of the invention are e.g. diisocyanates, suchas 2,4-tolylene diisocyanate (TDI), 2,6-tolylene diisocyanate, a mixtureof 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate,hexamethylene diisocyanate, cyclohexane-1,4-diisocyanate, xylylenediisocyanate, isophorone diisocyanate, 1,5-naphthalene diisocyanate,4,4′-diphenylmethane diisocyanate, 2,4′-diphenylmethane diisocyanate,2,2′-diphenylmethane diisocyanate, 4,4′-diphenyldimethylmethanediisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate,dicyclohexylmethane-4,4′-diisocyanate,dicyclohexylmethane-2,4′-diisocyanate,dicyclohexylmethane-2,2′-diisocyanate, methylcyclohexane diisocyanate,tetramethylxylylene diisocyanate, 2,6-diisopropylphenylene isocyanateand mixtures thereof. Hexamethylene diisocyanate is especiallypreferred. The aforementioned compounds are commercially available andare obtainable for example from the company Bayer MaterialScience AG.

Isocyanurates in the sense of the invention are compounds of formula(II)

where R¹, R² and R³ in each case independently of one another are—(CH₂)_(m)—N═C═O, —(CH₂)_(q)—[(C₆H₃)(Me/Et)₃(N═C═O)], and m=1-12, q=0-6and Me=methyl and Et=ethyl, wherein

-   R¹, R² and R³ are preferably identical.

The following compounds of formula (III)

and of formula (IV)

are preferred.

The aforementioned compounds are commercially available and areobtainable for example from the company Bayer MaterialScience AG.

Biurets in the sense of the invention are for example compounds offormula (V)

where R⁴, R⁵ and R⁶ in each case independently of one another are—(CH₂)_(p)—N═C═O, with p=1-12, wherein

-   R⁴, R⁵ and R⁶ are preferably identical.

In an especially preferred embodiment of the invention the biuret is acompound of formula (VI)

The aforementioned compounds are commercially available and areobtainable for example from the company Bayer MaterialScience AG.

Uretdiones in the sense of the invention are reaction products of atleast two isocyanates with formation of at least two dioxodiazetidinebonds:

Their preparation is known per se by a person skilled in the art and canfor example be carried out as described in EP 1 422 223 A1.

The uretdione can be a dimer, trimer, oligomer or polymer.

Suitable examples of uretdiones, which have an aliphatic orcycloaliphatic radical, are known per se by a person skilled in the artand corresponding monomeric uretdiones comprise for example isophoronediisocyanate, 1,4-cyclohexyl diisocyanate,1,1-methylene-bis(4-isocyanatocyclohexane),1,2-bis(4-isocyanatononyl)-3-heptyl-4-pentyl-cyclohexane andhexamethylene-1,6-diisocyanate. The use of isophorone diisocyanate andhexamethylene-1,6-diisocyanate is preferred.

Furthermore, it is possible within the scope of the present invention touse, as activator, a uretdione that is obtained starting from anaromatic isocyanate. This aromatic isocyanate preferably has 6 to 20carbon atoms, especially preferably 6 to 15 carbon atoms. Correspondingaromatic monomeric isocyanates can for example be selected from thegroup comprising 2,4-diisocyanatotoluene, 2,6-diisocyanatotoluene,1,5-naphthylene diisocyanate, 4,4′-methylene-diphenyl diisocyanate,1,3-bis(3-isocyanato-4-methylphenyl)-2,4-dioxodiazetidine,N,N′-bis(4-methyl-3-isocyanatophenyl)urea and tetramethylxylylenediisocyanate. Among these aromatic isocyanates, 2,4-diisocyanatotoluene,2,6-diisocyanatotoluene and 4,4′-methylene-bis(phenyl diisocyanate) arepreferred. 2,6-Diisocyanatotoluene and 4,4′-methylene-bis(phenyldiisocyanate) are especially preferred.

The aforementioned compounds are commercially available and areobtainable for example from the company Rhein Chemie Rheinau GmbH orfrom Bayer MaterialScience AG.

Allophanates in the sense of the invention are compounds of formula(VII)

These compounds are generally obtainable by reacting any startingcompounds containing urethane and/or urea groups, also containing unitsof the general formula (R″OOC—NHR′), with monoisocyanates of the generalformula R′″—NCO or with diisocyanates of the general formula OCN-A-NCO,where R′″ or A is preferably an alkyl radical with 1 to 20 carbon atomsor an aryl radical with 6 to 20 carbon atoms and R′ and R″,independently of one another, are an alkyl radical with 1 to 20 carbonatoms or an aryl radical with 6 to 20 carbon atoms.

Suitable monoisocyanates are any aromatic, aliphatic and cycloaliphaticmonoisocyanates with up to 20 carbon atoms, such as methylisocyanate,isopropylisocyanate, n-butylisocyanate, n-hexylisocyanate,cyclohexylisocyanate, stearylisocyanate, the optionally halogenatedphenylisocyanates, 1-naphthylisocyanate, the optionally chlorinated orfluorinated m-, o-, and p-tolylisocyanates, p-isopropylphenylisocyanate,2,6-diisopropylphenylisocyanate and p-toluenesulphonyl diisocyanate.

Suitable diisocyanates are any aromatic, aliphatic and cycloaliphaticdiisocyanates with 6 to 40 carbon atoms, preferably 6 to 15 carbonatoms, such as isophorone diisocyanate, 1,4-cyclohexyl diisocyanate,1,1-methylene-bis(isocyanatohexane),1,2-bis(4-isocyanatononyl)-3-heptyl-4-pentylcyclohexane,hexamethylene-1,6-diisocyanate, 2,4-diisocyanatotoluene,2,6-diisocyanatotoluene, 1,5-naphthylene diisocyanate,4,4′-methylenediphenyl diisocyanate,1,3-bis(3-isocyanato-4-methylphenyl)-2,4-dioxodiazetidine,N,N′-bis(4-methyl-3-isocyanatophenyl)urea and tetramethylxylylenediisocyanate. Of these, hexamethylene-1,6-diisocyanate is preferred.

The allophanates that are especially preferred within the scope of thepresent invention are compounds of formula (VIII)

where R^(IV) within the molecule can be identical or different anddenote C₁-C₆-alkyl, preferably —(CH₂)₆—, and R^(V) corresponds toC₁-C₆-alkyl.

Corresponding allophanates and production thereof are described forexample in EP 0 000 194 A1, whose disclosure in this respect isincorporated by reference in the present invention. The aforementionedcompounds are commercially available and are obtainable for example fromthe company Bayer MaterialScience AG.

Carbodiimides in the sense of the invention are preferably compounds offormula (IX)R¹¹—(—N═C═N—R¹²—)_(m)—R¹³   (IX),in which

-   m corresponds to an integer from 1 to 500,-   R¹²═C₁-C₁₈-alkylene, C₅-C₁₈-cycloalkylene, arylene and/or    C₇-C₁₈-aralkylene,-   R¹¹═R¹²—NCO, R¹²—NHCONHR⁹, R¹²—NHCONR⁹R⁷ or R¹²—NHCOOR⁸ and-   R¹³═—NCO, —NHCONHR⁹, —NHCONR⁹R⁷ or —NHCOOR⁸,-   where, in R¹¹, R⁹ and R⁷, independently of one another, are    identical or different and represent a C₁-C₆-alkyl,    C₆-C₁₀-cycloalkyl or C₇-C₁₈-aralkyl radical and R⁸ represents a    C₁-C₆-alkyl-, C₆-C₁₀ cycloalkyl- or C₇-C₁₈-aralkyl radical or    denotes a polyester or polyamide radical or    —(CH₂)_(l)—(O—(CH₂)_(k)—O)_(g)—R¹⁰,-   with l=1-3, k=1-3, g=0-12 and-   R¹⁰ ═H or C₁-C₄-alkyl.

Mixtures of carbodiimides of formula (IX), including the correspondingoligomers and/or polymers, can also be used, polymeric carbodiimidesbeing preferred.

The compounds according to formula (DC) are commercially available, e.g.from the company Rhein Chemie Rheinau GmbH or can be prepared by themethods that are familiar to a person skilled in the art, as describedfor example in DE-A-11 30 594 or U.S. Pat. No. 2,840,589 or by thecondensation of diisocyanates with cleavage of carbon dioxide atelevated temperatures, e.g. at 40° C. to 200° C., in the presence ofcatalysts. Strong bases or phosphorus compounds, for example, haveproved suitable as catalysts. Phospholene oxides, phospholidines orphospholine oxides and the corresponding sulphides are preferably used.Tertiary amines, metal compounds with a basic reaction, metal salts ofcarboxylic acids and non-basic organometallic compounds can also be usedas catalysts.

The aforementioned compounds are commercially available and areobtainable for example from the company Rhein Chemie Rheinau GmbH.

Blocked activators, preferably with lactams, especially preferablycaprolactam, or activators blocked with phenols, oximes and/or epoxidescan for example be produced by reaction of at least one compound offormulae (I) to (IX) with at least one lactam, caprolactam, phenols,oxime and/or epoxide at temperatures from 80 to 100° C. by the methodsfamiliar to a person skilled in the art.

Lactam-magnesium halides, preferably bromides, alkali-alumodilactamates, preferably sodium, alkali-metal and/oralkaline-earth-metal lactamates, preferably sodium, potassium and/ormagnesium, individually or mixed, can be used as catalysts in the senseof the invention.

The aforementioned catalysts are commercially available and areobtainable for example from the company Rhein Chemie Rheinau GmbH orfrom the company KatChem spol.s.r.o.

In one embodiment of the invention, mixture a) and mixture b) are addedtogether for polymerization at temperatures between 80 and 160° C.,preferably 100 and 140° C. Polymerization takes place by the processesthat are familiar to a person skilled in the art, as described forexample in Kunststoffbandbuch, Vol. 3/4, Technische Thermoplaste, HanserFachbuch, pages 413-430. During this, the mixture is preferably stirred.Mixing units, e.g. stirred reactors, can be used for this.

In another embodiment of the invention, further lactam and/or furthercatalyst and/or optionally further additives, such as impact modifiers,such as e.g. polyetheramine copolymers, glass fibres, continuous glassfibres, carbon fibres, aramid fibres and/or processing aids, such ase.g. high-molecular polyols, thickeners, such as e.g. aerosils, UV- andthermostabilizers, conductivity improvers, such as e.g. carbon blacksand graphites, ionic liquids, marking substances and/or colorants, areadded to mixture a) and mixture b).

Mixtures a) and b) are preferably used in proportions from 1:3 to 3:1,especially preferably in proportions of 1:1.

Production of mixtures a) and b) according to the invention preferablytakes place as follows:

-   a) Activator Mixture

For this, at least one activator of formulae I-IX is added to a lactammelt at temperatures between 70 and 120° C., preferably 80-100° C.,homogenized or pelletized on a pelletizing belt or flaked on a flakingroll.

-   b) Catalyst Mixture

For this, at least one catalyst, e.g. Na caprolactamate or a highlyconcentrated Na caprolactamate masterbatch, is added to a lactam melt attemperatures between 70 and 120° C., preferably 80-100° C., homogenizedor pelletized on a pelletizing belt or flaked on a flaking roll.

The aforementioned pelletizing belts or flaking roll are commerciallyavailable from the Sandvik Holding GmbH or GMF Gouda.

As an alternative, catalyst mixture b) can be prepared in concentrationsup to max. 5 wt % from the respective starting materials in lactam bydirect synthesis, for example as in the methods familiar to a personskilled in the art from lactam and Na methanolate with subsequent orsimultaneous removal of the solvent by distillation. The method can becarried out in batch mode and in continuous mode.

In one embodiment of the present invention, mixtures a) and b) areisolated after production, optionally dried, packed and stored. Thepacked material can be pulverized or crushed. The mixtures of lactam andactivator and/or catalyst prepared by the method according to theinvention are characterized by high storage stability (for more than 6weeks), so that the mixtures can be stored prior to use and can betransported to the place of use. It is thus possible to prepare themixture precisely for use and thus avoid fluctuations in compositionthat arise in mixtures prepared immediately before polymerization.

The present invention also relates to mixtures that are stable instorage, comprising at least one activator in a concentration up to max.5 wt % in at least one lactam and use thereof for the production of castpolyamides.

Activators in the sense of the invention are isocyanates, isocyanurates,biurets, allophanates, uretdiones and/or carbodiimides as the individualcompound or as a mixture and blocked activators and/or activators alsocontaining solvents, especially preferably biuret and/or isocyanate.

Regarding the mixtures according to the invention that are stable instorage, reference should be made to the above information about theactivator.

The present invention also relates to mixtures that are stable instorage, of at least one catalyst that is solid at temperatures up to80° C., in a concentration up to max. 5 wt % and a lactam and usethereof for the production of cast polyamides.

The invention also covers the use of a combination of the aforementionedmixture according to the invention that is stable in storage, of atleast one activator and at least one solid catalyst mixture that isstable in storage at temperatures of up to 80° C., for use in theproduction of cast polyamides.

Catalysts in the sense of the invention are lactam-magnesium halide,alkali-alumo dilactamate, alkali-metal and/or alkaline-earth-metallactamate.

Regarding the mixtures according to the invention that are stable instorage, reference should be made to the above information about thecatalyst.

The aforementioned mixtures according to the invention are preferablyused as a substitute for metal, e.g. in the automobile industry, in theproduction of electrical engineering components and for electronicpurposes, for the production of plates, rods, tubes, sheaves, pulleys,gear wheels and bearings and/or for container manufacture.

Regarding the mixtures according to the invention that are stable instorage, reference should be made to the above information about lactam.Compounds of formula (I) are preferred.

The scope of the invention encompasses all of the definitions ofradicals, indices, parameters and explanations stated generally or inpreferred ranges above and in the following taken together, thus alsobetween the respective ranges and preferred ranges in any combination.

In cases when the concentration of active substance in the mixture isabove the concentration of active substance intended for polymerization,further lactam can be added before the actual polymerization.

In cases when only the activator is used as mixture with the lactam,preferably the catalyst, optionally together with further lactam, isadded to the activator mixture during polymerization.

The following examples serve for explaining the invention, but withoutlimiting it.

EXAMPLES

Reagents:

-   Caprolactam dry (MP>69° C.) from the company Lanxess Germany GmbH,-   Activator Addonyl® 8108, a hexamethylene diisocyanate (HDI) biuret,    70% in N-ethylpyrrolidone, commercially available from Rhein Chemie    Rheinau GmbH,-   Activator Brüggolen C20 (approx. 35% HDI in caprolactam),    commercially available from the company Brüggemann GmbH,-   Addonyl® Kat NL from Rhein Chemie Rheinau GmbH, approx. 18% sodium    caprolactamate in caprolactam.    Execution and Measurement:-   Flask A: 196.8 g caprolactam and 3.2 g Addonyl® 8108, equivalent to    2.2 g HDI biuret (comparative example), prepared immediately before    measurement,-   Flask B: 192 g caprolactam and 8 g 18% Na caprolactamate in    caprolactam as Addonyl® Kat NL (comparative example), prepared    immediately before measurement,-   Flask C: 197.8 g caprolactam and 2.2 g HDI biuret (according to the    invention), stored at 90° C. for a period of: a) Flask C1: 1    week, b) Flask C2: 2 weeks, c) Flask C3: 6 weeks.-   Flask D: 200 g solid Batch-Ready® caprolactam with an Na    caprolactamate content of 0.8% (according to the invention),-   Flask E: 196.8 g caprolactam and 3.2 g Brüggolen® C20 (comparative    example), prepared immediately before measurement,-   Flask F: 200 g solid Batch-Ready® caprolactam with an HDI-biuret    content of 1.2% (according to the invention),-   Flask G: 200 g solid Batch-Ready® caprolactam with a HDI content of    1.2% (according to the invention),-   Flasks A to G were heated to 122° C. (±2° C.).

The melts thus obtained were worked up at 122° C. (±2° C.) in an oilbath under vacuum (<15 mbar) for 20 minutes. After aerating withnitrogen, the activator components (Flasks A, C, E, F and G) werecombined with the catalyst component (Flasks B and D) as listed in thefollowing table, in a three-necked flask, stirred briefly andtransferred to the 600 ml beaker. The temperature of the mould (beaker)was 160° C.

Immediately after bringing the melts together in a three-necked flask,temperature measurement was started. This was carried out using Testo175-T3 temperature measuring equipment with IR-Serial Interface.

For a period of 15 minutes, the temperature of the polymerizing lactammelt was measured and recorded every 10 seconds.

The curve of the temperature of the polymerization mixture versus timewas measured and the time point at which the temperature rise wasmaximum was determined (turning point on the temperature-time curve).The time from putting the reaction mixtures together up to the timepoint of the maximum temperature rise corresponds to the pot life.

Table 1 shows the results when using solid Batch-Ready® caprolactam ascatalyst mixture and Batch-Ready® caprolactam as activator stored inliquid form (90° C.), mixtures II), III) and IV) compared with thefreshly prepared activator/catalyst mixture (mixture I))

TABLE 1 T (max.) Examples Pot life [° C.] I) Mixture of A and B(comparative example) 300-500 s >190° C. II) Mixture of C1 and D(according to the 300-500 s >190° C. invention) III) Mixture of C2 and D(according to the 300-500 s >190° C. invention) IV) Mixture of C3 and D(according to the 300-500 s >190° C. invention)

As can be seen from comparison of the examples, storage even for aperiod of at least 6 weeks does not lead to any impairment of theproperties.

Table 2 shows the results for preparation of the solid Batch-Readyactivator mixtures compared with the activator mixture Brüggolen C20from the prior art.

TABLE 2 Activator Pelletizability Brüggolen C20 (comparison) very poorpelletizability 40% HDI biuret in caprolactam not pelletizable(comparison) Mixture F (according to the very good pelletizabilityinvention) Mixture G (according to the very good pelletizabilityinvention)

Table 3 shows the results when using the solid Batch-Ready caprolactamas activator and catalyst mixture compared with the prior art.

TABLE 3 Examples Pot life T (max.) [° C.] Mixture of E and B(comparative 300-500 s >190° C. example) Mixture of F and D (accordingto the 300-500 s >190° C. invention) Mixture of G and D (according tothe 300-500 s >190° C. invention)

Using the method according to the invention, it is therefore possiblefor activator and catalyst mixtures to be produced or preparedsolvent-free and technically simply, without the need for laboriousproportioning of small amounts of catalysts and activators in theprocess for production of cast polyamide parts. By adjusting therequired activator and catalyst proportions specifically and accurately,polymerization can always be carried out optimally, ensuring constantquality of the cast polyamide parts. Moreover, owing to simpler handlingof the required raw materials, with personnel costs minimized, themethod is more cost-effective and is more advantageous from thestandpoint of workplace safety.

What is claimed is:
 1. A method of production of cast polyamidescomprising: adding an activator, in an amount of up to 5 wt %, to afirst lactam melt at temperatures between 70 and 120° C., whereby anactivator mixture is formed and homogenized, isolated after production,and optionally pelletized on a pelletizing belt or flaked on a flakingroll; adding a catalyst in an amount of up to 5 wt % to a second lactammelt at temperatures between 70 and 120° C., whereby a catalyst mixtureis formed and homogenized and pelletized on a pelletizing belt or flakedon a flaking roll, and subsequently melting and mixing together saidactivator mixure and said catalyst mixture, thereby forming a meltmixture, and polymerized the melt mixture in a mould at temperaturesbetween 80 and 160° C.
 2. The method according to claim 1, wherein atleast one of the first lactam or the second lactom corresponds togeneral formula

where R represents an alkylene group with 3 to 13 carbon atoms.
 3. Themethod according to claim 1, wherein the activator comprises at leastone isocyanate, isocyanurate, biuret, allophanate, uretdione and/orcarbodiimid.
 4. The method according to claim 1, wherein in catalystcomprises at least one lactam-magnesium halide, alkali-alumodilactamate, alkali-metal and/or alkaline-earth-metal lactamate.
 5. Themethod according to claim 1, wherein the second lactam and/or catalystis added prior to melting.